java 随机生成字符串 （字母和数字）

public static String getRandomString(int length) { //length表示生成字符串的长度
String str = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
Random random = new Random();
StringBuffer sb = new StringBuffer();
for (int i = 0; i < length; i++) {
int number = random.nextInt(str.length());
sb.append(str.charAt(number));
}
return sb.toString();
}